The invention relates to a device capable of delivering modulatable side thrust in controlled manner for controlling aerospace vehicles such as missiles, launchers, or satellites, using the principle of propulsion by reaction or by ejection of gas.
The principle whereby an aerospace vehicle is controlled by devices that deliver modulatable lateral thrust, i.e. perpendicularly to the axis of the vehicle, in order to make it follow a controlled trajectory (force control) or in order to correct its attitude (moment control) is already well known. As a general rule, each modulatable thrust device comprises a valve fed by a gas generator and controlled by an actuator itself controlled by an on-board computer by means of electrical signals.
With valves that are axially symmetrical, it is conventional to use a moving needle whose position in the gas flow as controlled by a proportional actuator determines the through section for the gas leaving via a nozzle having a fixed diverging portion, and thus determines the level of thrust, on the basis of propulsion by reaction.
In conventional moving needle propulsion systems, a large fraction of the thrust is taken up by the wall of the diverging portion (surface integral of static pressure). The length of the fixed diverging portion therefore needs to be long in order to maximize thrust. However it is limited in practice by the need to take account of phenomena associated with matching external pressure, such that the length of the fixed diverging portion is the result of a compromise between those contradictory requirements. Conventional devices having a moving needle and a fixed diverging portion also present two drawbacks: relatively large size along the thrust axis and permanent failure to optimize the thrust produced, with those drawbacks being particularly severe in applications to vehicles of relatively small diameter whose altitude changes very considerably in flight, such as air-to-ground interceptor missiles.
An object of the invention is to propose modulatable lateral thrust devices for controlling aerospace vehicles, which devices are compact, in particular in the thrust direction, and consequently better suited to being integrated in vehicles, and are of smaller mass. In particular, an object of the invention is to propose modulatable lateral thrust devices capable of being integrated in vehicles while complying with the dimensional constraints thereof, such as limited outside diameter.
Another object of the invention is to propose thrust devices that are not only compact, but that are also capable of delivering optimal thrust whatever the external pressure, i.e. whatever the altitude.
To this end, the present invention provides a device comprising: a moving needle; a valve body having a chamber surrounding part of the needle, at least one gas admission opening out into the chamber, and a gas outlet opening out into the chamber and defined by a wall portion that co-operates with a portion of the nose of the needle to define an outlet section for gas leaving the chamber; and actuator means for controlling the position of the needle in the valve body by acting on a rear end portion of the needle; in which device the nose of the moving needle has an aerodynamic concave profile and the wall portion which defines the outlet from the chamber is shaped in such a manner as to be capable of directing the escaping gas essentially against the concave shape of the nose of the needle.
Thus, the needle performs simultaneously the function of a moving member that enables thrust to be modulated by adjusting the gas outlet section, and the function of the main member for taking up the thrust that is produced.
As a result, and contrary to conventional modulatable thrust devices, there is no need to extend the gas outlet from the chamber by a diverging portion, or to do so in a very short manner only. The lateral extent of the thrust device is consequently reduced, thereby making it possible to design vehicle having limited outside diameter. The means for actuating the needle act on the rear of the needle, so they are disposed on the inside and consequently do not encumber the periphery of the vehicle. In addition, the outgoing gas jet is confined at its periphery by the effect of the surrounding atmospheric pressure and it adapts automatically to variations in ambient pressure, thus always producing thrust that is optimal as a function of altitude.
An architecture for a self-adaptive thrust device with a central body in the form of an optionally truncated point having a concave aerodynamic profile and with a nozzle that is virtual at least in part is known per se, in particular as a xe2x80x9cexpansion-deflection nozzlexe2x80x9d or as an xe2x80x9caerospikexe2x80x9d, but in the field of propelling aerospace vehicle. In that field of propelling aerospace vehicles, it is suggested by patent U.S. Pat. No. 3,888,419 and U.S. Pat. No. 3,989,191 to provide a limited amount of variation in the intensity and the direction of the thrust by modifying the position of a front portion of a central metal body by means of hydraulic actuators housed inside it. The reliability of such a device exposed to hot gases would seem to be difficult to guarantee. Mention can also be made of patent U.S. Pat. No. 3,929,289 which describes an axial thrust device with a central body having an outer portion made of graphite. Thrust can be modulated by varying the axial position of a tube surrounding the central body, which requires external actuator means.
According to a feature that is advantageous in terms of compactness and ability of the thrust device of the invention to be integrated, the valve body is immersed in a propulsion gas generator. The valve body and the needle, which come into contact with the hot gases, are preferably made of thermostructural composite material, in particular a composite material having a ceramic matrix such as a C/SiC composite material (carbon fiber reinforcement densified by a matrix of silicon carbide).
According to another feature of the thrust device of the invention, the actuator means are of the proportional type, enabling the thrust to be modulated over the entire range of full to none. The actuator means are of the electromechanical type, for example, and they can be connected to the needle by a rotary shaft fitted with an eccentric engaged in a peripheral groove in the rear end portion of the needle.
According to yet another feature of the thrust device of the invention, the actuator means are thermally insulated from the hot gases flowing in the body of the valve.